Ultra-low-noise supercontinuum generation with a flat near-zero normal dispersion fiber

A pure silica photonic crystal fiber with a group velocity dispersion (β₂) of 4  ps²/km at 1.55 μm and less than 7  ps²/km from 1.32 μm to the zero dispersion wavelength (ZDW) 1.80 μm was designed and fabricated. The dispersion of the fiber was measured experimentally and found to agree with the fiber design, which also provides low loss below 1.83 μm due to eight outer rings with increased hole diameters. The fiber was pumped with a 1.55 μm, 125 fs laser and, at the maximum in-coupled peak power (P₀) of 9 kW, a 1.34-1.82 μm low-noise spectrum with a relative intensity noise below 2.2% was measured. The numerical modeling agreed very well with the experiments and showed that P₀ could be increased to 26 kW before noise from solitons above the ZDW started to influence the spectrum by pushing high-noise dispersive waves through the spectrum.